Heat activated fabric treatment compositions for use in an automatic tumble dryer are described in our co-pending applications, WO-A-03/087285 and WO-A-03/087286, and devices suitable for use in the treatment fabrics in a tumble dryer are disclosed in our co-pending applications, WO-A1-02/33160 and WO-A1-02/33161.
In order to optimise the delivery of the active material onto fabrics during the drying cycle, it is desirable to provide a fabric treatment composition which, at a temperature below the heating cycle temperature of the tumble dryer, remains substantially within a dispensing article and is capable of undergoing a transition during the heating cycle of a tumble dryer such that it can be dispensed from the dispensing article.
It is, therefore, desirable to provide a fabric treatment composition which is capable of undergoing such transitions without unacceptable instability. It is particularly desirable that the composition can undergo such a cycle repeatedly.
Effective delivery of such a fabric treatment composition requires the composition to be flowable at the delivery temperature (i.e. the heating temperature of the tumble dryer).
Accordingly, it is desirable to provide a heat activated fabric treatment composition which can be delivered as a liquid during the heating cycle of a tumble dryer from a dispensing device.
It is further desirable to provide a heat activated fabric treatment composition which can be stored in a dispensing device and which can undergo repeated cycles from a more viscous storage state to a less viscous dispensable state such that during the heating cycle of the tumble dryer at least part of the composition is delivered to fabrics and during the storage state does not leak from the device.
The problem of leakage becomes a significant risk when the ambient storage temperature is close to the melting temperature of the composition.
Our copending British Patent Application No. 0420202.4 discloses a heat activated fabric treatment composition comprising:                (a) from 1 to 75 wt % of a quaternary ammonium fabric softening system which comprises:                    (i) a quaternary ammonium fabric softening material derived from a parent fatty acid or acyl compound having an average iodine value of from 0 to 19, and            (ii) a quaternary ammonium fabric softening material derived from a parent fatty acid or acyl compound having an average iodine value of from 20 to 140                        (b) from 5 to 60 wt % of a nonionic surfactant; and        (c) from 5 to 70 wt % of water, and its use in conditioning fabrics in a tumble dryer.        
That composition addresses some of the above-mentioned problems.